ABSTRACT The innate and injury specific heterogeneity associated with mild to severe TBI has made it challenging to identify clinical and therapeutic targets where intervention can meaningfully reduce the acute effects of injury and improve the long term recovery trajectory. One factor that contributes both to the heterogeneity associated with the TBI injury complex and recovery is the presence or absence of polytrauma, along with the complexity of trauma care required to manage injury related procedures and complications that arise. Little data exists regarding psychosocial outcomes after polytrauma, but existing reports suggest worse outcomes for those with polytrauma recovering from TBI versus TBI alone. Our previous works show that severe extracerebral injury (ECI) increases the propensity for suicidal endorsement (SE) over the long term among individuals who receive inpatient rehabilitation. The long-term goal of this project is to improve effectiveness and efficiency of mental health monitoring, resource access, and treatment for individuals with TBI and ECI through early identification of those at greatest risk for SE and with the greatest need for more intensive follow- up services. In attaining this goal we believe intervention will improve health, function, and quality of life. Our long-term hypothesis is that identifying acute to chronic care recovery pathways will allow for personalized screening, triage, and treatment strategies to reduce SE, increase life role participation, and improve health- related life quality after TBI. To address these hypotheses, we propose 1) to characterize demographics (age/sex), acute care complexity (complications, procedures, length of stay), and outcomes (SE, employment, substance use) among those with TBI, without/with ECI. 2) Identify demographic (sex, age) and psychosocial (employment, substance abuse) factors that influence the relationship between ECI and SE after TBI. 3) determine whether acute care complexity factors explain relationships between ECI and psychosocial outcomes and SE after TBI. The proposed research utilizes a unique large TBI database derived from a merger of the National Trauma Data Bank (NTDB) and the TBI-MS National Database allowing, for the first time, a comprehensive investigation of how acute trauma factors can affect long-term psychosocial outcomes after TBI. This novel, merged dataset has already allowed the association of ECI and suicidality to be ascertained and provides the impetus to further characterize important causal and inferential factors that drive SE. At project conclusion, we will illustrate an acute to chronic care causal pathway by which ECI, and associated innate, co-occurring acute care complexity, and psychosocial factors lead to SE after TBI. The work will inform future monitoring, prevention, and treatments that provide a personalized approach to mental health service access, and recovery after TBI. These data will support future work examining personal biology, and its interaction with environmental and psychosocial factors, with depression and suicidality etiologies after TBI.